Typical examples of a catalyst electrode (counter electrode) used in a dye-sensitized solar cell are platinum electrodes in which chloroplatinic acid is applied to and heated on an electrode substrate, and in which platinum is vapor-deposited or electro-deposited on an electrode substrate. In addition, an I2/I3− based redox system, which demonstrates well-balanced performances, is a typical example of an electrolyte used in a dye-sensitized solar cell.
However, a problem has been reported that platinum serving as a catalyst is dissolved in an electrolyte solution having an I2/I3− based redox system or similar system (see NPL 1, paragraph 0004 and so forth of PTL 1).
Several techniques for addressing such a problem are reported.
For example, PTL 1 discloses an electrode including a π-conjugated conductive polymer layer formed as a corrosion-resistant conductive coating material on an intermediate layer made of a platinum group metal layer and/or an oxide layer thereof formed on a substrate. As the corrosion-resistant conductive coating material, polypyrrole, polyaniline, polythiophene, or derivatives thereof are exemplified.
Moreover, PTL 2 filed by the same applicant as PTL 1 above discloses, as a highly corrosion-resistant catalyst electrode, a catalyst electrode having a corrosion-resistant conductive layer on a metal layer on a catalyst electrode. As the material for forming the corrosion-resistant conductive layer, various metal oxides, metal nitrides, and metal borides are exemplified.
Further, PTL 3 mainly targets a fuel cell, and does not mention a dye-sensitized type solar cell, but states that elution of platinum can be prevented by supplying a reactive gas containing a heterocyclic compound, for example, pyridines such as bipyridine, terpyridine, and phenanthroline to an electrochemical cell to bring the reactive gas into contact with a platinum-containing electrode catalyst layer in the electrochemical cell.
Furthermore, PTL 4 can be cited as an example similar to PTL 1 above in terms of materials for an electrode, even though PTL 4 does not particularly mention the durability and thermal resistance of an electrode. PTL 4 discloses an electrode in which a conductive layer containing platinum particles and a conductive binder for binding the platinum particles is formed on a substrate and the voids in communicating with a surface of the conductive layer are formed among the platinum particles, especially in order to surely obtain a large surface area for the electrode surface. As the conductive binder, polythiophene such as poly(3,4-ethylenedioxythiophene), polypyrrole, and polyaniline are exemplified.